CAPTURING TAGGED RED SALMON 

 WITH PULSED DIRECT CURRENT 



by 



Richard B. Thompson 



U. S. Fish and Wildlife Service 



Seattle, Washington 



ABSTRACT 



The equipment, installation, and techniques of operation of an experi- 

 ment to collect individual fish from schools of migrating adult red salmon 

 (Oncorhynchus nerka) in Alaska with pulsating direct current are described. 

 Electrodes were installed in the river in the path of the salmon. Current 

 was turned on as the selected fish passed between the electrodes. Fish 

 between the electrodes were forced to move towards the positive electrode, 

 placed in slack water 3 feet deep close to shore. As they encountered the 

 denser electrical current, the fish were electronarcotized and final capture 

 was made with a long-handled dip net. Trial collections resulted in captur- 

 ing 83 percent of the individual fish for which attempts were made. Tests 

 to determine optimum pulse frequencies and duty cycles indicated that fre- 

 quencies between 60 and 140 per second and duty cycles between 40 per- 

 cent and 85 percent gave good results. A pulse rate of 90 per second at 

 80-85 percent duty cycle gave the best general results. 



Separation of Asian and North American 

 stocks of salmon on the high seas is one 

 of the most pressing problems now facing 

 biologists working on research and man- 

 agement of our salmon resources. Red 

 salmon, Oncorhynchus nerka, is one of the 

 most important fish species involved. 



In 1956 a full-scale tagging program 

 was undertaken on the high seas for the 

 American Section of the International 

 North Pacific Fisheries Commission. The 

 Fisheries Research Institute of the Uni- 

 versity of Washington was awarded con- 

 tract No. 14-19-008-2424 by the U.S. 

 Fish and Wildlife Service (since con- 

 tinued by the Bureau of Commercial 

 Fisheries) to conduct a high-seas salmon 



tagging program. Recovery of a tagged 

 fish on its upstream migration would 

 indicate the -natal side of the Pacific 

 for that fish. 



In the 1958 tagging and recovery op- 

 erations, 13,000 fish were tagged and 

 released at a total cost of $256,000. The 



1958 recovery was 112 tagged fish; the 



1959 recovery, from the same lot, was 

 57. It is possible that more will be re- 

 ceived from Asiatic waters, raising the 

 total recoveries to an estimate of 200. 

 Some minor additional returns of tags 

 in I960 from all areas are expected. 

 Thus, it is indicated that each recovered 

 tag will have cost about $1,300 in actual 

 expenditures. The value of a recovered 

 tag, because of the few recoveries and 



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